A major cost factor in the manufacture of nuclear grade zirconium and hafnium metals from zircon sand is the production of metal scrap during fabrication processing. This scrap has already incurred the entire production cost of converting zircon sand to metal ingot from the following operations: Chlorination, Purification (Iron Removal and Condensation), Separation, Precipitation, Rechlorination, Sublimation, Reduction, Distillation (for MgCl.sub.2 and Mg removal), Double Arc Melting.
A significant manufacturing cost benefit could be realized if a process were available to separate zirconium metal from alloy scrap and to recycle it as metal without having to repeat all the manufacturing steps of the conversion process.
Modifications to the reduction process have been suggested in many U.S. Pat. Nos., including 4,511,399; 4,556,420; 4,613,366; 4,637,831; and 4,668,287, assigned to the same assignee.
Molten (fused) salt electrochemical (electrolytic) processes for deposition of metal on one electrode (with evolution of chlorine gas at the other electrode) are known in the art. U.S. Pat. Nos. 3,764,493 to Nicks et al. (utilizing a porous diaphragm), and 4,670,121 to Ginatta et al. are examples of such processes.
A high temperature process using zirconium tetrachloride as a part of a molten salt bath and reducing zirconium from the chloride to the metal (molten salt systems mentioned were potassium-zirconium chlorides and sodium-zirconium chlorides) is suggested in U.S. Pat. No. 2,214,211 to Von Zeppelin et al. A relatively high temperature process using zirconium tetrachloride as a part of a molten salt bath and introducing magnesium to reduce zirconium from the chloride to the metal (with external electrolytic reduction of magnesium from the chloride to the metal, to recycle magnesium) is suggested in U.S. Pat. No. 4,285,724 to Becker et al. Another high temperature process using zirconium tetrachloride as a part of a molten salt bath and which introduces sodium-magnesium alloy to reduce zirconium from the chloride to the metal (with a molten salt of magnesium chloride and sodium chloride is suggested in U.S. Pat. No. 2,942,969 to Doyle. Using zirconium tetrachloride as a part of a molten salt bath and preferably introducing aluminum (but possibly magnesium) to reduce zirconium from the chloride to the metal, generally with the aluminum being introduced dissolved in a molten zinc is taught by Megy in U.S. Pat. No. 4,127,409. Electrolytic-refining (metal in, metal out purification, rather than reduction from the chloride) processes are suggested in U.S. Pat. Nos. 2,905,613 and 2,920,027. (Note especially, "Electrorefining Zirconium," Baker et al., Bureau of Mines TN23-U7 No. 5758, 1961, on a sodium chloride-potassium fluorozirconate electrolyte.)
Direct electrolysis of zirconium has been reported in a all-chloride molten salt systems, in mixed chloride-fluoride systems, and in all fluoride systems (Martinez et al., Metallurgical Transactions, Vol. 3, Feb. 1972-571; Mellors et al, J of the Electrochemical Soc., Jan. 1966-60). All-metallic deposits were obtained from fluoride-containing baths (e.g. at 800.degree. C. using sodium fluorozirconate), but the efforts to plate out of all-chloride baths always produced a significant amount of subchlorides.